This invention relates to the use of a liquid crystal material to selectively control light transmission through a transparent or semitransparent panel, and more particularly to the use of a liquid crystal material to provide a window shade of adjustable transmittance, in combination with a dual-pane, heat-insulating window panel (thermal-pane window).
Thermal-pane windows conventionally make use of spaced dual panes to provide a thermal barrier restricting heat conduction between the outside and the inside of a building and therefore tending to reduce heating and cooling costs. To further reduce cooling costs, window shades or blinds are used to block out intense, direct rays of sunlight, since conventional windows, insulating or otherwise, have little effect on radiative heating. However, in using a conventional shade to eliminate solar glare, the view to the outside is blocked, which may be considered a visually unattractive result. U.S. Pat. No. 4,268,126 discloses a three pane window unit that overcomes this limitation without sacrificing energy efficiency by providing an electro-optical shade as an integral part of a thermal pane window. The room occupant may select the degree of light transmittance of the shade, thus eliminating glare and the adverse effect on cooling requirements from direct rays of the sun, while not blocking the view to the outside.
The present invention makes use of liquid crystal material to provide adjustable control of the intensity of light transmission through a multi-pane, thermal window unit. Generally, use of liquid crystal materials to selectively control light transmission through a transparent panel is known. Representative patents disclosing the nature of liquid crystal materials and their use are U.S. Pat. No. 3,322,485 to Williams, entitled "Electro-Optical Elements Utilizing an Organic Nematic Compound", U.S. Pat. No. 4,005,928 to Kmetz, entitled "Nematic Liquid Crystal Displays for Low Voltage Direct Current Operation", and U.S. Pat. Nos. 4,268,126 and 4,456,335 to Mumford entitled "Thermal Pane Window With Liquid Crystal Shade." New applications requiring improved window constructions have necessitated efforts to develop thermal window units that are lighter and more easily fabricated.